The present invention relates to flexible couplings, and in particular, it relates to flexible couplings for connecting drive shafts.
Drive shafts that are used in variable velocity situations have problems that differ greatly from a constant velocity situation. One problem of great importance in a variable velocity situation is shock loads which are delivered both to the drive shaft and to the component being run by the drive shaft. Such shock loads are detrimental to the drive shaft, and especially to the component that is being run by the drive shaft, such as a pump.
The equipment is also subject to abuse from harmonic resonance. All rotating equipment has one or more natural torsional frequencies. When the system's speed corresponds to one of these natural frequencies, resonance occurs. At these resonant speeds, the amplitude of system vibrations is greatly magnified. The resonance can quickly destroy bearings, mounts and other connected equipment, including the drive shaft. Next to catastrophic overloads, operating in a resonance condition is probably the fastest way to destroy rotating equipment.
The problem of shock loads is further compounded when the drive shaft includes a coupling. Such couplings are needed, for example, to perform maintenance on either the component that is being run, such as the pump, or on the motor that is used to run the pump. Oftentimes, the drive shaft is joined together by a shear pin. However, this type of an arrangement is not suitable where shock loads occur frequently since the shear pin will have to be replaced frequently. In addition, such a shear pin connection does not provide for easy re-connection of the two drive shafts, especially when either the motor or the component that is being run has been removed for maintenance.
Another arrangement that is commonly used to connect two drive shafts are conventional universal joints. Examples of such joints are illustrated on pages 16 and 17 of the Pictorial Handbook of Technical Devices by P. Grafstein et al, Chemical Publishing Co., New York, 1971. However, for the most part, these types of universal joints directly transmit shock loads and may themselves be harmed or fatigued over time because of such shock loads.
Another type of coupling is described in U.S. Pat. No. 1,485,036 granted to Kingsley. The Kingsley patent describes a universal joint that connects two shafts. The joint includes a coil spring engaging threaded end portions of two shafts and is disposed about a ball and socket arrangement that also connects the two shafts. Rotative movement between the shafts is transmitted through the coil of the spring. Although the arrangement described in the Kingsley patent absorbs shock loads better than conventional constant velocity U-joints, the coil spring described in the Kingsley patent simply transmits rotational movement and does not provide for dampening shock loads. For example, the Kingsley patent states that "driving torque will be transmitted through the spring with the maximum efficiency and without distortion of any of the parts.revreaction..